Implantable leads having externally exposed ring or band electrodes can be used to deliver electrical stimulation to surrounding tissue and/or to sense electrical energy produced by the surrounding tissue. Such leads are often implanted, for example, within the epidural or intrathecal spaces of the spinal column, along peripheral nerves, within the brain, and about the heart. Electrical stimulation of the spinal cord has been shown to be effective in relieving intractable pain in some patients. Such electrical stimulation can reduce or eliminate the use of pain relieving drugs.
One such lead is formed of polymeric material, for example, polyurethane or silicone. The lead can be nominally 1 mm in outer diameter and about 20 cm in length. A typical lead may have a series of electrodes formed as bands or rings disposed in a spaced apart relationship in a lead distal region. The distal region of the lead can be introduced, for example, into the epidural region for use in stimulation of the spinal column. The lead proximal region may have a corresponding set of band or ring connectors or terminals, one for each corresponding electrode in the distal region. Each proximal region terminal can thus be connected to one distal electrode in a typical configuration.
The terminals can be used to couple the proximal end of the lead to a lead extension, which can in turn be coupled to an implantable pulse generator (IPG). The lead extension can provide added length to extend the reach of the lead to a more distantly placed IPG. In some embodiments, the lead extension is between about 20 and 50 cm in length.
The lead typically has a lumen extending from the proximal end through to the distal region, with the lumen being dimensioned to accept a stiffening member or stylet. The lead, commonly formed of a polymeric material and being very small in cross section, is typically very floppy and not pushable. With a stylet or stiffening member inserted, the lead gains the needed pushability, and can be advanced into and up the spinal column to the desired location.
In use, a large gauge Toughy needle can be inserted into the spinal column and into the spinal canal. The stylet is then inserted into the lead, and the now stiffened lead advanced through the needle and up into the spinal canal. When the distal region of the lead is in the proper position, the stiffening member can be removed and the introducing needle also removed, leaving the proximal end of the lead protruding from the patient.
A small incision can then be made near the site of entry of the lead, in order to direct the proximal end of the neurological lead back into the body to be mated to a lead extension or to the IPG. The proximal end of the lead extension is coupled to the proximal end of the lead, and electrical continuity established. The lead extension is used to extend the useful length of the lead sufficient to reach the implanted IPG, which can be, for example, 20-50 cm distant. With the length increased by the extension, the free end of the extension can be inserted into the incision and into the body.
In one procedure, known as “tunneling”, an elongate, flexible metal device is used to form a tunnel or passageway under the skin, for example, around the torso, to the site of the implanted or soon to be implanted IPG. This tunneling procedure can be used to form the passageway for the extension, which is then advanced through the passageway and to the IPG site.
The extension, while adding length, also adds complexity and cost. It also adds yet another required step for the treating physician to perform. Increasing the lead length to do away with the need for the extension would be desirable. However, with current leads, the stiffening member or stylet would likewise have to be increased in length. While this is possible, a significantly longer lead having a stiffening member within would be somewhat unwieldy. For example, a 50 cm long stylet inserted within a 50 cm long lead would be difficult for the treating physician to maneuver. This aspect is significantly limiting, given that the treatment site is the spinal cord, where care must be exercised.